The long-pulse alexandrite laser has a similar mode of action as the ruby laser, but the former is thought to have several advantages [89]. The use of the 755 nm wavelength allows for deeper penetration into the dermis. However, there is a 20% reduction in the absorption of the laser light at this wavelength compared to that seen at 694 nm [60,90]. The longer pulse width of 20 ms is closer to the thermal relaxation time of the hair follicle (40-100 ms) which may more selectively heat the hair follicle [91]. The longer pulse width allows for better cooling of the epidermis, since it is much longer than the relaxation time of the melanin in this portion of the skin (3-10 ms) [52].
Garcia et al. in a study of subjects with skin types IV-VI pretested the treatment area and used posttreatment topical corticosteroids to reduce any posttreatment inflammation [ 68 ]. With these precautions, almost 3% of the subjects had side effects. A study comparing long – and short-pulsed alexandrite photoepilation found that erythema, edema, crusting, and pigmentation changes were more noticeable with the long pulse alexandrite lasers [92]. In addition, induction of hair growth was seen in 3% of those subjects treated with the LP-Alex on the face and neck sites [93]. Studies that have been done on Asian subjects have found satisfactory reduction in hair density. Side effects in these reports have ranged from 1 to 3%, and have included crusting, folliculites, and pigment changes. These side effects are reported to be minimal and transient in this subset of subjects with darker skin [92]. Moreno-Arias et al. report long-lasting hypopigmentation in one subject with Type III skin after a single treatment. The author reports that this may be due to long-lasting melanocyte suppression in this subject [94]. A multicenter prospective study found that mild and short-lived acneform reactions occurred in 6% of subjects undergoing laser hair removal. The acneform lesions are most likely to occur in young, dark-skinned individuals treated with Nd:YAG laser. History of PCOS, number of prior treatments, use of aloe vera cooling gel, and the sex of the patient were not correlated with the development of these lesions (Table 8.2) [94].